The present invention relates to systems for purification of engine exhaust gases and more particularly to an arrangement for directing flow of secondary air discharged from an air pump to a reactor installed in an exhaust system of an internal combustion engine.
It is known to use an air pump as a source of secondary air and to direct flow of secondary air to a suitable point in an engine exhaust system for promoting oxidation reaction of HC and CO contents of the engine exhaust gases within a reactor installed in the exhaust system, the reactor including a thermal reactor, a manifold reactor. It is the common practice, in an exhaust gas purification system, to use an air pump which has a far greater capacity than required in the system in order to compensate for a drop in the pump capacity after a long use. Directing all of secondary air from the air pump to a reactor over the whole operating conditions of an engine to which the purification system is connected is not desirable. If all of the secondary air is supplied to the reactor when the engine operates under light road load, the reactor temperature will be lowered to make it difficult to maintain sufficient oxidation of CO and HC contents. If under this condition rich air fuel mixture is fed to the engine to provide exhaust gases rich enough to react with overabundance of oxygen, the reactor temperature will rise excessively and fuel consumption will increase. To solve this problem it has been practiced to relieve a portion of the secondary air from the air pump to the atmosphere under the control of control means. The control means becomes complicated in construction if flow rate of the secondary air supplied to the reactor is to be precisely controlled. On the other hand, fuel consumption of the engine increases if a carburetor setting is rich to permit rough control of the flow rate of the secondary air supplied to the reactor.